Ruminant Nutrition: Carbohydrates and Lipids

摘要

The transition from pregnancy to lactation imposes a large degree ofmetabolic stress on dairy cows, when the overall negative energy balancecauses lipolysis and release of fat in the form of nonesterified fattyacids (NEFA). In prior studies, we proved that circulating NEFA activatethe peroxisome-proliferator activated receptors (PPAR) in a hybrid in vitro-in vivo model, where immortalized cells were treated with serum atdifferent NEFA concentrations. PPAR are involved in the metabolism offatty acids and triglycerides (TAG), as well as in the regulation of insulinsensitivity, all crucial processes in the peripartum. Our objective was toassess the role of PPAR activation in the transition period through an exvivo bovine liver model. Our hypothesis was that activation of PPAR,measurable through changes in gene expression, would be modulated byserum NEFA through the peripartum. Four primiparous Jersey cows receivedtrocar biopsies at −10 and + 10 DIM, and the tissue was sectionedusing a Krumdieck Tissue Slicer to obtain thin slices (PCLS) suitable forculture. Two PCLS were then incubated with each treatment: NEFA isolatedfrom serum, as well as whole serum, and isotype-specific syntheticagonists and antagonists of PPAR, applied individually. Transcriptionof PPAR target genes was measured via RTqPCR, and analyzed throughPROC MIXED of SAS 9.4, comparing treatment and DIM effect, andtheir interaction. Despite large variation between animals, expression ofPPARA, PPARG and FABP1 decreased while transcription of PDK4 increasedfrom −10 to +10 DIM. Treatment with a PPARγ agonist increasedexpression of ACADVL and LIPC at +10 DIM. NEFA and a PPARδ antagonistdecreased PDK4 expression, and C 16:0 upregulated transcriptionof FABP1. Whole-transcriptome sequencing revealed that treatmentof PCLS with PPAR agonists in the postpartum modulates the expressionof genes involved in lipid metabolism, as well as amino and nucleicacid metabolism. Despite the changes in gene expression, no change wasobserved in the TAG concentration in response to PPAR activation. Ourfindings suggest that our PCLS model is informative at a molecular level.